I. Field of the Invention
The present invention relates to pressure vessels and, in particular, to a pressure vessel having a plurality of filter bags mounted therein for filtering liquid material.
II. Description of the Prior Art
The prior art is replete with examples of filtering devices and means for retaining a filtering device within a secured position until removal of the same is desired. An example of pressure vessels having a plurality of filtering elements secured therein is disclosed in U.S. Pat. No. 3,503,516 issued on Mar. 31, 1970. This patent discloses a pressure vessel having a top wall provided with a plurality of openings through which are fitted a plurality of filtering elements. The individual filtering elements are secured to the top wall by a plate member that overlays each of the filtering elements and through which a plurality of fasteners extend into engagement with the top wall. In use it is necessary to remove these filtering elements, and the pressure vessel disclosed in the above-listed patent requires the time-consuming and necessarily difficult task of removing each of the fasteners so as to first remove the overlying plate in order to gain access to each of the individual filtering elements for their removal.
This difficulty is overcome by a number of methods. One example of a method employed for overcoming the difficulty encountered in the U.S. Pat. No. 3,503,516 design is disclosed in U.S. Pat. No. 4,022,693. This patent suggests the use of a cover that has an offset portion that spans the housing top wall, with the offset portion therein being spaced above each of the filtering elements to provide a flow path communicating an inlet to each of the filtering elements. The cover in the '693 patent has a peripheral lower face portion that overlays a section of each filtering element so as to retain the filtering elements in position when the cover is closed. Removal of the cover permits immediate access to the filtering elements and their removal.
A second example of a pressure vessel which overcomes the aforementioned problem is that disclosed in U.S. Pat. No. 1,619,118. This patent discloses a vessel similar to the vessel disclosed in the '693 patent in that the cover when removed from its closed position permits immediate access to the filtering elements carried therein.
In both of the above-mentioned examples, there is a necessity to have both a sealing engagement between the cover and the housing and a sealing engagement between the filtering element and the top wall surface which is supporting the filtering element, otherwise fluid will leak past the filtering element in an unfiltered condition. This problem is compounded in the '693 vessel by the fact that both seals are obtained by engagement of the housing cover with the housing wall and the filtering element. This requires rather high-quality engineering tolerances which greatly increase the cost of manufacturing such equipment, which normally must be made and marketed at a relatively low price in order to be competitive. Thus, the ease of obtaining and removing the filtering elements as described in the two aforementioned patents so as to overcome the problems in the '516 vessel creates a new problem in obtaining a proper seal which, if not proper, can greatly damage the article on which the filtered fluid may be used. For example, it is common to use pressure vessels of this type for filtering paints used in the manufacture of automobiles. If unfiltered paints are sprayed on an automobile, an improper coating will result, necessitating repainting of the automobile.
An example of how the problems with this seal arrangement may be overcome is disclosed in the Miller U.S. Pat. No. 3,319,793. This patent utilizes a plurality of springs to hold filtering elements in place. While this achieves the desired result of having immediate accessibility to the filtering elements, it requires the manufacture of specialized filters; and their use in a market which is highly competitive is not at all advantageous.